The invention relates to a camera for recording television, photographic or cinematographic images, including an automatic focus-setting device, in which camera an image of a scene to be picked up is obtained via an optical lens system of an opto-electronic sensor in the form of a charge transfer device suitable for television comprising a pick-up member, an information storage member and a parallel-in, series-out shift register member connected to a sensor output terminal, said camera operating for the automatic focus-setting with first and second optical paths of different path lengths in the optical lens system, said camera including a signal comparator for comparing signals to be supplied by the sensor from the output terminal, which signals are associated with the presence of the first and second optical paths of different path lengths, the focus-setting device adjusting the focus-setting in a substantially optimum manner dependent on the result of comparison.
A camera of this type, particularly for use in television is described in U.S. Pat. No. 4,301,478. FIG. 10 of the Patent shows an embodiment of the charge transfer device in the form of a so-called frame transfer device and FIG. 11 shows an associated embodiment of the signal comparator. The Figures show that on a specific part of the scene sensor, outside the part on which the scene image is present for the conversion into a picture signal for display, two scene images are made via the optical paths of different path lengths. To this end the optical lens system comprises a prism having a semi-transmissive surface area and a fully reflective surface area. The singly passed light and the twice reflected light originate from the optical path having the shortest and longest path lengths, respectively. In the signal comparator the picture definition of one scene image is compared with that of the other for focus-setting, whilst the focus-setting is modified to obtain an optimum signal correlation. Furthermore the Patent describes that the different optical path lengths may be consecutively present in time. To this end the use of a disc rotating around a shaft and having the form a half a circle sector and consisting of transparent glass or a synthetic material is described, which disc rotates in front of the specific pick-up member which is used for obtaining the information for the focus-setting.